1. Field of the Invention
This invention concerns an ignition system that is applicable to a fuel injection type internal combustion engine.
2. Description of the Prior Art
Internal combustion engines which make use of fuel injection have been developed in combination with ignition systems in order to take advantage of the opening of the injector valves so as to trigger an ignition spark. Such spark assists in the combustion of the fuel. However, it has been found difficult to avoid spurious signals that are created when the injector valve opens since it is not a clean electrical circuit break or switch opening which is created.
One prior approach to the difficulty has been described in a copending application assigned to the same assignee as this application, i.e. Ser. No. 200,753 filed Oct. 27, 1980, now U.S. Pat. No. 4,342,305, which is a continuation of Ser. No. 048,867 filed June 15, 1979. It involved a lockout circuit arrangement which would stop any additional signals created by the injection valve after the initial opening for a predetermined period of time. However, it was found that the injection of fuel takes place over a fixed number of crank shaft degrees of rotation and consequently, at low engine speeds a fixed time delay represented only a few crank shaft degrees while at high speeds it included many crank shaft degrees of rotation. Consequently, the fastest engine speed was determined by the fixed time the system was locked out, and this is an undesirable feature.
In another approach to the problem, some of the principles indicated in circuits disclosed by a U.S. Pat. No. 3,926,165 were employed in order to have a lockout circuit which would lockout the spark signal for a fixed number of crank shaft degrees. However, in that arrangement a difficulty was found in the case where the lockout happened to exceed the maximum permissable lockout. For example, in a four cylinder engine the maximum lockout is ninety degrees, in a six cylinder it is sixty degrees and in an eight cylinder engine, it is forty-five degrees. And, if the injection should not take place on one cycle (such as under deceleration conditions) the lockout circuit would react as if the engine had only one half the number of cylinders so that the circuit would lockout every other firing pulse. The engine would then run on only one half the number of cylinders.
Furthermore, it has been found in practice that needle bounce by the injector valve sometimes continues (at full throttle) until just a few degrees before the next cylinder injects. Consequently, it is an object of this invention to provide an improved lockout circuit for use in the generation of spark signals created at the injection of fuel upon opening of an injector valve.